The feeding and handling of particulate material, in the form of bed material and fuel, which is supplied to a combustor, in the form of a pressurized fluidized bed, present difficult problems and are achieved with present-day technique by mixing the particulate material with water and pumping in the material in the form of a paste, or by pneumatic transport of particulate material. In the latter case, according to known technique, a feeding system in the form of a locking system is used, which comprises valves and intermediate containers, a so-called lock-hopper system.
In a PFBC (Pressurized Fluidized Bed Combustion) power plant the fluidized bed may operate at a pressure of the order of magnitude of 20 bar, and therefore a feeding system comprising valves is exposed to great stresses resulting in a rapid deterioration of the sealing capacity of the valves. The service life becomes short and the maintenance costs become high.